I shake from time to time but not nearly every 2 weeks.
At the extreme end, I’ve left Black resin, that had expired, sitting on a dark, room temperature shelf for many months (maybe a year?). Trying to print after that long without shaking led to failures (and even pouring any out could wind up spoiling the whole cartridge because the components aren’t evenly mixed and maybe you just poured out most of your actuator / pigment / whatever). But shaking for a good 20 minutes produced results that were almost as good as new.
That was with the old Black v2… my impression is Black v4 doesn’t have the same longevity.
These days I have a resin mixing “rotisserie” and from time to time do a ‘remixing day’ where I’ll put each of the cartridges I have in inventory in it for 10 mins each to keep them homogenized. But I’m not always the most diligent about it. Does not doing it reduce the lifespan? Who knows, maybe; I haven’t done any empirical comparisons. I imagine Formlabs has, then published its recommendations based on their observations but with a wide safety margin.
I’d be curious if Formlabs’ own warehouses are shaking cartridges every two weeks (I’ve received resin that was manufactured several months prior so I know in at least some causes their turnover isn’t fast enough to make it irrelevant). I’ve certainly seen shelves of resin at resellers that perhaps sit there for months (just a guess) without any special TLC.
Personally I think your resin management plan is likely better than the vast majority of other customers out there (but of course I invite others to jump in and refute that).